The proposed research will develop a detailed computer model of the human heart. The model, specifically designed for microcomputer utilization and with extensive use of graphics, will be commercialized for research, commercial, and educational purposes. The Specific Aims of the proposed research are: 1) model development, including implementation of rate and time at rate dependencies for refractory time and conduction time, implementation of drug effects, implementation of pacing modes, and implementation of accessory pathways; 2) improved input/output facilities, to clearly illustrate the behavior of the model; 3) validation of the model against experimental data in the literature; 4) preparation of a plan for Phase II research and final report. The model development is strongly health- related through its future (Phases II and III) impacts in the areas of pacing and detailed predictions of drug effects. It is suggested that even after Phase I, through improved modeling capability, the costs of research efforts should be reducible, both in dollars and in terms of animal subjects. The proposers believe that the only similar model development is taking place outside the United States, with much less emphasis there on widespread applicability through user friendliness and graphical output.